A vertical substrate processing apparatus has been used as a substrate processing apparatus which performs a heat treatment with respect to a plurality of wafers in a batch. In the vertical heat treatment apparatus, wafers are accommodated in a processing vessel and a process gas is supplied from a gas supply part to the wafers so that heat treatment is performed on the wafers.
As a vertical heat treatment apparatus, a configuration is used in which an exhaust port is formed in a sidewall of a processing vessel having a plurality of exhaust zones divided in an arrangement direction of wafers, and a gas introduction pipe for supplying a process gas is installed at a position opposite to the exhaust port with the wafers interposed between the gas introduction pipe and the exhaust port.
However, in such an apparatus, since the exhaust port is formed below the processing vessel, the process gas introduced into the processing vessel is likely to flow downward. As such, a flow of the process gas may be biased to one side within the processing vessel. This degrades in-plane uniformity when performing a heat treatment with respect to a plurality of wafers accommodated in the processing vessel.